Boolean with bevel bezier curve
So why can't I use bool on a simple bend cylinder? It is even meshed!

In your screenshot it's not a mesh. You can't use the boolean modifier with a curve object, even if it's beveled. You have to first convert it to a mesh.

I am not a Python developer, so I don't know how to perform that step in code, but that is likely what your problem is.
Edit: Here is another question that has a Python implementation.